Dissolved gas analysis ( DGA ) is widely used to detect incipient faults in transformers. A brief review on the interpretation of DGA in transformers is presented, with a special emphasis on the Duval Triangle method. It is shown how the accuracy of DGA laboratory results can affect the reliability of DGA diagnosis. The minimum gas levels in service above which diagnoses may be attempted are indicated, as well as the gas levels observed before failure.
Several methods of interpretation of DGA in transformers in service are provided in IEC Standard 605991, the IEEE Guide C57.1042, as well as in published reviews on the subject.
The Duval Triangle method is described in the IEC Standard and in these published reviews, however, users sometimes are not quite at ease with the use of triangular coordinates. One purpose of this paper is therefore to indicate in more detail how to use such coordinates. Another purpose is to present the most recent developments made at CIGRE concerning gas levels in service.
This paper is limited to DGA in transformers. It does not address the case of DGA in load tap changer (LTC) accessories, for which specialized diagnostic programs are available, or which is treated elsewhere.
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